1. Field of the Invention
The invention relates generally to a hybrid control system for regulation of the output of a process or a plant, and to perform discrete control functions.
2. Background of the Invention
U.S. Pat. No. 3,697,957 relates to a self-organizing control system. The control system combines statistical decision theory, prediction theory, and rapid trial generation to determine future control actions. The system includes on-line sampling and changing of the system operation. Performance assessment units are included, and a "probability state" variable unit is included for the control operation. The probability state variable unit may be broadly construed as a "fuzzy" logic controller in this context.
U.S. Pat. No. 4,587,470 relates to a multiplex control system having a backup controller. In case of an abnormal condition, control is switched from the main controller to a secondary controller. An interfacing means is provided for providing a time lag to prevent tracking of control data. The control system addresses difficulties in tracking computational data for a system including main and subsidiary controllers of different hardware structures, such as analog and digital devices in combination. Thus, this reference addresses the problem of providing two differing control structures to assure reliability.
U.S. Pat. No. 4,628,462 relates to a power plant which includes a detailed model as well as a multiplane control system. Optimization results are calculated off-line recurrently. Several models are included in the system, and the system includes overrides.
U.S. Pat. No. 4,639,853 relates to an adaptive switching on-off controller. A model is used, and a manufacturing system is shown.
U.S. Pat. No. 4,661,911 relates to an adaptive constant refiner having an intensity control. This reference teaches adaptive control with a control algarhythm.
None of the references cited teaches the combination of a primary controller which is an adaptive direct digital controller as a primary expert controller, together with a backup controller which is a "fuzzy" expert controller, with the control function being transferred by an interface system which includes a simulator that performs a soft diagnosis, with learning expert units storing correct control action for direct application and to provide a reference for the interface system.